The present invention relates generally to canopy type doors and more particularly to canopy doors of a single or double leaf construction suitable for use in buildings having large openings, such as airplane hangers, wardhouse docks, or garages.
Due to the large surface area of large canopy doors, one of the problems associated with their use has been to adequately stabilize the door against wind gusts, particularly when the door is in the fully closed position. Extensible diagonal bracing struts have been used to stabilize bifold doors in the area near the joint of the two leaves; and various stops have been used to stabilize the lowermost portion of the lower leaf.
One of the most critical problems associated with large canopy doors has been the difficulty of achieving the initial opening of the door. The opening cables are spaced close to the plane of the door when the door is in the closed position to yield a simple, uncluttered design. The close spacing of the cables to the door leaves, however, results in a relatively short moment arm which makes it difficult to initially break the door to swing it upward on its horizontal axis.
The prior art shows bracing struts used to provide an initial outward force. Specifically, U.S. Pat. No. 2,936,830 shows a strut having a cable attached to exert an essentially upward force on the strut which results in an initial outward force applied to the door. This structure, however, creates an upward deflection of the strut which must be overcome by the cable in opening the door. Further, this repeated deflection could result in structural damage to the strut.
Those concerned with the above problems recognize a need for a canopy door having an improved stabilizing means and an improved initial opening mechanism.